A 79-year-old woman presented with a 1-year history of gradual neurologic decline involving confusion, memory loss, imbalance, and incontinence. On examination, she was oriented only to self and had mild nonfluent aphasia. CT performed without the administration of contrast material revealed a large left frontotemporal mass with areas of calcification. CT angiography and magnetic resonance imaging also revealed the mass (which measured 3.8 cm by 6.2 cm by 3.9 cm) without contrast enhancement or intraluminal filling, which raised suspicion of a thrombosed aneurysm that was likely to have originated from the bifurcation of the middle cerebral artery. Bands of different T2-weighted signals suggested previous episodes of layering of blood products. Conventional angiography and three-dimensional reconstruction revealed no residual aneurysm and an occlusion of the anterior division of the middle cerebral artery as a result of compression mass effect, along with retrograde filling from leptomeningeal collateral branches of the anterior cerebral artery (see the Supplementary Appendix). After discussion with the patient’s family, a decision was made to conservatively manage the aneurysm and to address the hydrocephalus with the placement of a ventriculoperitoneal shunt and endoscopic transfrontal septostomy. An improvement in the patient’s overall neurologic status was noted at a clinic follow-up visit.Source: https://www.nejm.org/doi/full/10.1056/NEJMicm1513571